The present invention is related to and represents an improvement over the subject matter disclosed in applicant's U.S. Pat. No. 5,024,195. The disclosure of U.S. Pat. No. 5,024,195 is incorporated by reference into this application.
The present invention relates to multi-fuel compression-ignition internal combustion engines wherein liquid fuels of varying viscosity can be delivered to the engine under high pressure. A secondary fuel with high ignition qualities is used to start and warm up the engine When the engine has warmed up, a primary fuel is used to operate the engine. The invention is an improvement over the engine disclosed in the aforementioned patent in that the firing pressure can be effectively regulated by the rate of fuel injection.
There are two types of internal combustion engines based on the method of ignition thereof, namely spark-ignition engines and compression-ignition engines, the latter of which may also be designated as autoignition engines. A spark-ignition engine requires fuel with high volatility and high octane number. A compression-ignition engine requires fuel with a high cetane number and a certain amount of viscosity. The efficiency of a spark-ignition engine is limited by the allowable compression ratio which is determined by the octane number of the fuel used therewith. The specific engine output of a compression-ignition engine is limited by the peak firing pressure due to a high compression ratio required for producing the high compression air temperature necessary for compression ignition. Neither of these two types of engines can be designed for optimum specific engine output.
The ignition delay of a compression-ignition engine leads to a large fuel accumulation in the combustion chamber when the combustion process begins. As a result, the firing pressure in the combustion process cannot be controlled. The current method of operating a compression-ignition engine employs a high cetane fuel in conjunction with a high compression ratio. A high compression ratio without the elimination of the ignition delay creates a high firing pressure which is detrimental to the engine reliability and specific engine output. It is therefore highly desirable to provide an engine employing a new type of ignition which can greatly reduce the ignition delay so that the firing pressure can be regulated by the rate of fuel injection to obtain optimum specific engine output.